JPH10246712A - Apparatus for allowing insulating sample in analytical instrument to have nearly uniform surface potential - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniform a surface potential of an insulating sample by projecting electron beams of low energy to a sample area while a projection area outside a radiation area is kept in a negative charge stage and directing positive ions to the projection area near the radiation area. SOLUTION: X rays 6 illuminate a radiation area 12 of a sample 2, whereby photoelectrons are emitted. An electron gun 7 projects electrons of low energy to the sample 2, and a charged particle source 10 projects positive ions 11 of low energy of not larger than about 10eV to the sample 2. Both the electron gun 7 and the charged particle source 10 are controlled by a computer 13. The radiation area 12 is positively charged because of the emission of photoelectrons. A projection area 14 to which low energy electrons are projected is larger than the radiation area 12, including the radiation area 12, and therefore positive charges are neutralized. However, excessive negative charges are produced in an area outside the radiation area 12. For neutralizing the excessive negative charges, beams of positive ions 11 are projected to a part 16 of the area near the radiation area 12. A surface potential of the sample 2 can be schematically uniformed according to the method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling the surface potential of an insulating sample during surface analysis.

The present invention relates generally to surface analysis, and more particularly to electron and ion emission spectroscopy, such as x-ray photoelectron spectroscopy and secondary ion mass spectroscopy, and more particularly to controlling the surface potential of an insulating sample. , So that such a spectroscopic analysis can be performed.

[0003]

2. Description of the Related Art In an x-ray photoelectron spectroscopy (XPS) apparatus, a portion of a sample is irradiated with an x-ray beam to emit electrons (for example, see US Pat. No. 5,315,511).
No. 3 (Larson et al.). These radiations are analyzed using an energy analyzer to determine surface components. However, in an insulating sample, electrons are emitted from a positively charged surface in the x-ray irradiation area. The positive charge is
It varies across the surface, affecting the emitted electron energy and the trajectory, and errors are introduced during the corresponding analysis.

[0004] In secondary ion mass spectroscopy (SIMS), a surface is illuminated with positive ions, thereby emitting atoms and ions from the surface. The incident ions form a positive charge on the insulating sample. In the case of x-ray photoelectron spectroscopy (XPS), such charges
Errors occur during analysis.

Various solutions to this problem include, at least in the case of x-ray photoelectron spectroscopy (XPS), a grid inserted near the sample to smooth out the potential gradient (US Pat. No. 4,680,467). No. (Bryso
n)). However, this leads to the introduction of interfering elements and thus limits the area of applicability.

In another solution, the sample is neutralized by irradiating it with low energy electrons. This provides a technically significant improvement, but generally illuminates an area larger than the light-emitting area, so that it is non-uniformly neutralized and thereby has excess in the area outside the optoelectronic area. Negative charge is supplied. U.S. Patent Publication No. 543234
No. 5 (“Kelly patent”) discloses that a magnetic field gradient is smoothed by discharging negative excess charges using irradiation of ultraviolet rays or positive ion beams. This technique using radiation or ions can significantly reduce the gradient, but some gradients remain and affect the analysis. That is, the above-mentioned US Pat. No. 5,432,345 (“Kelly p.
Attent ") is primarily for ultraviolet radiation, and little is disclosed about the use of positive ions. Ion sources are commonly used for sputtering and the like,
It typically produces high energy ions of 10 eV or more (although low energy devices have been used empirically).

A general problem with existing x-ray photoelectron spectroscopy (XPS) equipment is that it is sensitive to the operating conditions of the neutralizer, even with the use of electron irradiation. It becomes difficult to obtain a reproducible photoelectron peak position and peak shape.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an x-ray photoelectron or secondary ion emitting device in which a sample has a radiation region for receiving an energy beam and emits radiation from the sample. , So as to generate a positive charge in the radiation region). Another challenge is some residual of the gradient (albeit smaller than that caused by the background art described above).
To make a certain surface potential substantially uniform.

[0009]

SUMMARY OF THE INVENTION The foregoing objects are at least partially achieved by irradiating the device with a low energy electron beam at a sample area having an emission area to neutralize a positive charge; During the irradiation, the irradiation area outside the emission area is solved by providing electronic means that are brought into a negatively charged state. Further, the apparatus is provided with ion means for directing positive ions at least to a part of the irradiation area in the immediate vicinity of said emission area to neutralize the negative charges in said part.

[0010]

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, an electronic means is configured to generate an electron beam with a low energy of less than about 2 eV and an energy spread of less than about 0.5 eV. In a preferred embodiment, electronic means is provided which is formed from an electron emitting material having a work function of less than about 2 eV and has a thermionic electron emitter for generating a low energy electron beam.

In another embodiment, advantageously, in combination with a low energy electron beam, the ions are substantially reduced to 10
It is configured to have ion energy smaller than eV. In another embodiment, advantageously in combination with a low energy electron beam and a low ion energy, the electronic means is spaced at a predetermined distance from the sample and the electron beam is defined at a predetermined position on said sample. And the ratio of the distance to the diameter is less than about 10.

[0012]

In the examples, devices useful in the present invention are utilized with x-ray photoelectrons (XPS) for surface analysis (see, for example, the aforementioned US Pat. No. 5,513,113 (“Larson patent”)). The insulating sample 2 (FIG. 1) is mounted in a vacuum chamber of an x-ray photoelectron spectroscopy (XPS) apparatus 4. 6 is normally directed toward the sample, where the x-rays illuminate the emitting area or spot 12 (FIG. 2) on the sample and deliver photoelectrons (not shown). Electron gun 7
Sends out low energy electrons 8 and irradiates the sample.
The charged molecular source 10 directs a beam of positive ions 11 toward the sample. The electron gun and the ion source are advantageously provided by a computer (see U.S. Pat.
arson patent ").

The emission region 12 is positively charged by the emission of photoelectrons from the sample surface. The region 14 illuminated by the low energy electrons is larger than and includes the emitting region, thus neutralizing the positive charge, but creating an excess of negative charge in the region outside the emitting region. . The ion beam 11 is directed to at least a portion 16 of this region, near the emission region, to neutralize the negative charge. In this figure, the ion beam is directed to a region that is equal to or smaller than the irradiated region, although the region of positive ions is shown to be larger than the electron irradiated region 14 (where Significant regions around the emission region are covered by the ion beam, effectively minimizing potential gradients within and around the emission region). In a typical x-ray photoelectron spectroscopy (XPS) spectrometer, the x-ray emission region 12 is 1 mm or less in diameter and the electron region 1
4 has a diameter of 1 to 10 cm, and the ion region 16 has a diameter of 10 to 50 cm.

According to one embodiment of the present invention, the ions of beam 11 have a low ion energy of substantially less than 10 eV. In a suitable ion gun (FIG. 3), ionization chamber 18 has a thermionic filament 20, which emits electrons, which
Accelerated by the positive potential of the tubular lattice 22 ionizes the argon gas therein. The emission current is measured by a grid ammeter 23. The gas passes through a regulated inlet 24 from a gas supply 26 to a room pressure of about 25 mPa.
The pressure is applied to the ammeter 3 of the chamber 18 acting as the extraction electrode.
Detected by 0. Following the opening 19 in the ionization chamber, a cylindrical condenser lens 31, an opening 36, a pair of beam bending plates 32, a cylindrical objective lens 33, and a cylindrical assembly 4-pole to 8-pole deflection plate 34 as an option for path control.
Is provided. The tube 38 having these members is set at a relatively low floating voltage.
The ions are accelerated from the high voltage grid 22 through the tube and penetrate into the grounded conical exit ring 40, where
The sample 2 is irradiated with the ground. The lens voltage is detected as a percentage of the beam voltage. In the tube 38, a bend of about 5 ° is provided at the position of the curved plate 32 so as to remove neutral atoms from the ion beam. The foregoing arrangement, while indicating a suitable ion source, may utilize an advantageous or desired low energy source (which may be compatible with the equipment used).

According to another embodiment, the irradiated electrons have a relatively narrow energy spread, which is substantially less than about 0.5 eV, for example about 0.3 eV. Thus, advantageously, the electrons have a very low energy, advantageously less than 2 eV (compared to a spread of about 1-10 eV for normal irradiation). The electron gun 7 (FIG. 4) typically has a thermionic emitter 42 heated by an electric current, with the emitted electrons being of the desired energy accelerated through a cylindrical extractor 44. In an advantageous way to achieve spreading, the emitter 42 is formed from an electron emitting material having a work function, for example at 1 eV, of less than about 2 eV. By way of comparison, a typical tungsten emitter has a work function of about 4.5 eV. At a low work function, the emitter is operated at a low temperature, thereby substantially reducing the energy distribution and the width of the split at the high energy end of the Boltzmann distribution. For example, the emitter may be formed from a barium-strontium oxide film 46 on a platinum disk 48 heated by current at support legs 49 welded to the disk. This film is likewise advantageously formed on a nickel container used for the emitter in a vacuum tube. Suitable emitters are model ES-015 barium oxide disc cathode, Kimball Physic
s Inc. Wilton, NH.

Alternatively, the desired energy spread is:
An electron energy filter, such as a hemispherical electrostatic analyzer 50 (FIG. 5) disposed between the electron source, eg, thermionic emitter 42 'and the sample (optionally having one or more intermediate lenses 52). To achieve this.
Such a filter may be an electrostatic or electromagnetic energy analyzer configured for this application, such as a cylindrical electrostatic analyzer,
Alternatively, it may be a hemispherical electrostatic analyzer (as shown) of the type disclosed in the aforementioned US Pat. No. 5,513,113 (“Larson patent”).

The maximum current of irradiated electrons at the sample is limited by the space charge in the immediate vicinity of the sample, and its maximum value is determined by the ratio of the distance L between the electron gun and the sample to the diameter of the irradiated electron beam of the sample. It is inversely proportional to the square of L / D. This diameter is generally about the same as the diameter of the exit of the electron gun. Ratio L /
D is advantageously less than about 10, more preferably 6
Should be smaller, where D is the beam diameter at the exit of the electron gun.

It is particularly advantageous to use a combination of at least two, preferably all, of the above-described embodiments. Thus, in an advantageous embodiment, the ion energy is approximately 10
and less than about 2 eV with a narrow energy spread of less than about 0.5 eV achieved with a low work function emitter, the ratio of electron gun distance to beam diameter is , Less than about 10. Even more advantageously, the irradiating electrons are formed with an electron emitter having a work function less than about 2 eV.

In the improved embodiment described above, US Pat.
It has been found that the potential is substantially more uniform than the potential disclosed in US Pat. No. 4,432,345 (“Kellypatent”). That is, the device is significantly more robust and more reliable than the prior art, where the range of the sample type and the assertion area are determined by the analytical results and the sensitivity of the set electron emission current described above. Can be analyzed without change. A high irradiation current density can be achieved by using an electron gun with a low electron energy and a short distance. The photoelectron density is about 40 nA / 40 for a focused 10 micron diameter x-ray beam spot on an insulating sample.
reach mm ^2. In the case of neutral electron flow, it is advantageous to have at least 10 times greater than the photoelectron current, so that by means of the combined refinement,
400 nA / mm ² can be reached.

Similarly, the present invention provides a method for neutralizing an insulated sample with another analyzer (eg, a secondary ion mass spectrometer (SIMS) that irradiates the surface with positive ions) to bring the sample surface into a positively charged state. Used to transform Electron irradiation and introduction of low energy positive ions are performed substantially in the same way as x-ray photoelectron spectroscopy (XPS). In FIG. 1, x
Line 6 has been replaced by a beam of positive ions (separated from the neutralized beam of ions 11).

Although the present invention has been described with reference to the above specific embodiments, various modifications and changes may be made within the spirit of the present invention, and the scope of the dependent claims will be apparent to those skilled in the art. . Accordingly, the invention is only limited by the dependent claims and the equivalents thereof.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of the apparatus of the present invention.

FIG. 2 is a diagram showing the surface of the sample of FIG. 1;

FIG. 3 is a schematic diagram of an ion gun used in the apparatus of FIG.

FIG. 4 is a schematic diagram of an electron gun used in the apparatus of FIG.

FIG. 5 is a schematic diagram of an embodiment with a source incorporating an electron energy filter instead of the electron source of FIG. 1;

[Explanation of symbols]

 2 Sample 4 X-ray photoelectron device 6 X-ray 7 Electron gun 8 Low energy electron 12 Spot 10 Charged particle source 11 Positive ion 12 X-ray emission area 14 Electron irradiation area 16 Ion area 20 Thermal ion filament 22 Tubular lattice 26 Gas supply unit 32 Beam bending plate 34 Deflection plate 40 Ring 42 Thermal ion emitter 44 Cylindrical extractor 48 Platinum disk 50 Hemisphere electrostatic analyzer 52 Intermediate lens

Claims (19)

[Claims] An apparatus for obtaining a substantially uniform surface potential on an insulating sample in an analytical instrument, said sample acting on radiation from said sample so as to generate a positive charge in an emission area. A device having a radiation area for receiving an energy beam, comprising electronic means and ion means, wherein the electronic means lowers the sample area having the radiation area to neutralize the positive charge. Irradiating with an electron beam of energetic electrons, the irradiating region outside the radiating region being in a negatively charged state during the irradiating, and the ion means is configured to emit positive ions at least in the immediate vicinity of the radiating region; Directing a portion of the illuminated area to neutralize negative charges in said portion;
Apparatus, wherein said electronic means is configured to generate an electron beam with a low energy of less than about 2 eV and an energy spread of less than about 0.5 eV. 2. The electronic means includes an electron source and an electron energy filter, wherein the electron energy filter is disposed between the electron source and a sample to generate a low energy electron beam. The device of claim 1, wherein 3. The method of claim 1, wherein the electronic means comprises a thermionic electron emitter, wherein the thermionic electron emitter is formed from an electron emitting material having a work function less than about 2 eV and generates a low energy electron beam. Item 1. The apparatus according to Item 1. 4. The apparatus of claim 3, wherein the ions have an ion energy substantially less than 10 eV. 5. The electronic means is spaced at a predetermined distance from the sample, the electron beam having a predetermined beam diameter at the sample, wherein the ratio of the distance to the diameter is 5. The apparatus of claim 4, wherein said apparatus is less than about 10. 6. The apparatus of claim 5, wherein the energy beam is an x-ray beam and emits photoelectrons to generate a positive charge. 7. The electronic means is spaced at a predetermined distance from the sample, the electron beam has a predetermined beam diameter at the sample, and the ratio of the distance to the diameter is 4. The apparatus of claim 3, wherein said apparatus is less than about 10. 8. The apparatus of claim 1, wherein the ions have an ion energy substantially less than 10 eV. 9. The electronic means is spaced from the sample at a predetermined distance, the electron beam has a predetermined beam diameter at the sample, and the ratio of the distance to the diameter is The apparatus of claim 8, wherein said apparatus is less than about 10. 10. The electronic means is spaced at a predetermined distance from the sample, the electron beam has a predetermined beam diameter at the sample, and the ratio of the distance to the diameter is The apparatus of claim 1, wherein the apparatus is less than about 10. 11. The apparatus of claim 1, wherein the energy beam is an x-ray beam, thereby emitting photoelectrons to generate a positive charge. 12. The apparatus of claim 1, wherein the energy beam is a positive ion beam, thereby generating a positive charge. 13. An apparatus for obtaining a substantially uniform surface potential on an insulating sample in an analytical instrument, said sample acting on radiation from said sample so as to generate a positive charge in an emission area. A device having a radiation area for receiving an energy beam, comprising electronic means and ion means, wherein the electronic means lowers the sample area having the radiation area to neutralize the positive charge. Irradiating with an electron beam of energetic electrons, the irradiating region outside the radiating region being in a negatively charged state during the irradiating, and the ion means is configured to emit positive ions at least in the immediate vicinity of the radiating region; Directing a portion of the illuminated area to neutralize negative charges in said portion;
The apparatus wherein the ions are configured to have an ion energy of substantially less than 10 eV. 14. The electronic means is spaced at a predetermined distance from the sample, the electron beam has a predetermined beam diameter at the sample, and the ratio of the distance to the diameter is The apparatus of claim 1, wherein the apparatus is less than about 10. 15. The apparatus of claim 13, wherein the energy beam is an x-ray beam, thereby emitting photoelectrons to generate a positive charge. 16. The apparatus of claim 13, wherein the energy beam is a positive ion beam, thereby generating a positive charge. 17. An apparatus for achieving a substantially uniform surface potential on an insulating sample in an analytical instrument, said sample acting on radiation from said sample so as to generate a positive charge in the emission area. A device having a radiation area for receiving an energy beam, comprising electronic means and ion means, wherein the electronic means lowers the sample area having the radiation area to neutralize the positive charge. Irradiating with an electron beam of energetic electrons, the irradiating region outside the radiating region being in a negatively charged state during the irradiating, and the ion means is configured to emit positive ions at least in the immediate vicinity of the radiating region; Directing a portion of the illuminated area to neutralize negative charges in said portion;
The electronic means is spaced at a predetermined distance from the sample, the electron beam has a predetermined beam diameter at the sample, and the ratio of the distance to the diameter is about 1
An apparatus characterized by being less than zero. 18. The apparatus of claim 17, wherein the energy beam is an x-ray beam, such that the energy beam emits photoelectrons to generate a positive charge. 19. The apparatus of claim 17, wherein the energy beam is a positive ion beam, thereby generating a positive charge.